A thin film containing titanium, zirconium, or hafnium is used as an electronic member of electronic components, such as high dielectric constant capacitors, ferroelectric capacitors, gate films, barrier films, and gate insulators, and an optical element of optical communication devices, such as optical waveguides, optical switches, and optical amplifiers.
Processes for forming the above-described thin film include MOD techniques including a dipping-pyrolysis process and a sol-gel process and chemical vapor-phase growth techniques, such as chemical vapor deposition (hereinafter abbreviated as CVD) and atomic layer deposition (hereinafter abbreviated as ALD). Chemical vapor phase growth techniques involving vaporization of a precursor, such as CVD and ALD, are the most suitable for many advantages, such as compositional controllability, excellent step coverage, suitability to large volume production, and capability of hybrid integration. Metal compounds having an organic ligand are used as a precursor in CVD or ALD.
Metal nitride thin films having titanium, zirconium, or hafnium as a metal are used as a coating layer for enhancing the hardness and strength of, e.g., cutting tools, and gate films and barrier films of semiconductor devices. A number of techniques for fabricating these thin films by chemical vapor phase growth have been reported.
Patent document 1 (see below) discloses a process for forming a metal nitride and/or metal carbide thin film using a halide of titanium, zirconium, hafnium, vanadium, niobium, or tantalum. Patent document 2 (see below) describes a CVD process for forming a thin film of titanium nitride using titanium tetrachloride and ammonia gas.
Patent documents 3 to 5 propose processes for depositing a group 4 metal-containing thin film using, as a titanium, zirconium or hafnium precursor, a dialkylaminometal compound having an organic amine as a ligand, disclosing use of ethylmethylamine as the ligand.
However, the film formation process using a chloride typified by titanium tetrachloride needs high temperatures of at least about 500° C. Such a high temperature is unsuitable in the production of a semiconductor device element, such as a gate film. Although the organic amide metal compound having an organic amine as a ligand is capable of forming a metal nitride thin film at low temperatures, it is difficult for the resulting film to exhibit electrical characteristics as expected because of its high residual carbon content and to be applied to a gate film, a barrier film, or an electrode film that are particularly required to have electrical conductivity.
Patent document 6 (see below) teaches a process for forming a titanium nitride thin film by CVD using Ti(N(CH3)2)3X, Ti(N(CH3)2)2X2, Ti(N(C2H5)2)3X, or Ti(N(C2H5)2)2X2 (wherein X is a halogen atom). These titanium compounds are described as being easily thermally decomposable and suited for use as a gate film forming material. However, Ti(N(CH3)2)3Cl and Ti(N(CH3)2)2Cl2, which are representatively used in patent document 6, are solid and need to be maintained at a temperature at or above the melting point when used as a CVD material. They, while having good thermal decomposability, have poor thermal stability and can decompose during being heated to be kept in a liquid state for a long period of time. If used as it is a solid, there arise problems with the material vapor feed and in-line transportation of the material, such as shortage of vapor feed or variation in vapor feed with time. The problem of contamination with particles also occurs. Even in a process using a solution, such as a solution CVD process using a solution of a solid precursor in an organic solvent, the solution suffers from precipitation due to change in temperature, partial evaporation of the solvent, and change in concentration in a vaporizer, resulting in clogging of feed piping. The problem of the feed rate change with time due to, e.g., clogging of feed piping and the problem of contamination with particles remain to be completely settled down.    Patent document 1: JP 2003-64475A    Patent document 2: JP 7-201779A    Patent document 3: Korean Patent 156980    Patent document 4: JP 2006-45083A    Patent document 5: JP 2006-182709A    Patent document 6: JP 2000-36473A